Technical Question about road draft tube vs PCV

As I see it old engines with road draft tubes had an oil filler/vent at the front.

PCV equipped engines seem to have a vent (sometimes also the oil filler) in one valve cover and the PCV in the other.

So road draft engines pull air "front to back" through the lifter valley. PCV systems pull air past the rockers on one side, through the lifter valley, and past the other rockers.

Somewhere in my distant past I seem to remember hearing that without moving air through the valve covers that sludge can build up under the valve covers.

I'm wanting to install my pristine Corvette valve covers on my 350 using an old intake manifold that has the filler/vent at the front and figuring out where I can drill the manifold at the rear to install a PCV. It seems to me that what results will function basically just like the old road draft systems did.

Am I making a mistake?????

b-t-w; don't tell me to muck up the Vette VCs cause it ain't happnin. I can always leave the old M/T valve covers on it that have filler/vent/PCV in them.

Also on the 401 nailhead that I'm having built I want to do the same thing with filler/vent at the front and drilling the valley cover at the back. I really like the first (I think) generation nailhead valve covers that have no holes in them.

 

That lack of air movement allows condensation to form which can convert into sludge....

 

X2 ^_^^_^

 

Like @Crazy Steve said, moving air through the engine helps to remove the combustion by-products that "blow by" the rings. The blowby g***es include moisture in the form of water vapor, and also acids that can cause damage to engine components, and shorten oil life.

****ing as much of that blowby out of the engine and replacing it with fresh air makes for a much longer lived engine.

 

Flathead ventilation entered at the back and escaped at the front tube.

 

^^^^^^I was kinda planning a similar set up on my 283.
Put a PCV at the road draft tube location at the back of the block and plumb that to the intake.
My intake also has the vent/oil fill
Using no hole script covers

 

Used with an inline PCV

 

If you're building a car to drive to work every day, for several years, under all sorts of conditions, and parking it out in all kinds of weather, you might want to have the modern system with ventilation on the two valve covers. But if you're like most of us and don't put a lot of miles on the car, and change the oil more often than it really needs, and store it inside, and drive it when the weather's nice, you'll be just fine with whatever vent system you come up with. Don't sweat it too much.

 

Just as a point of reference, this particular subject has been discussed in a lot of threads over the years. A quick search for PCV locations and fuction should yield a lot of information.

 

I agree with Jim. The pcv in the back & vent in the fill tube works moderately well, it's better than a road draft system, and not as good as a system ventilating from one valve cover to the other. With the 63 - 67 system really only the lifter valley area gets ventilated, leaving fumes and moisture that rise into the valve covers there to ac***ulate. Running the pcv in one valve cover with a breather in the other prevents that ac***ulation of bad fumes & moisture.

 

I did exactly what you are contemplating. I didn’t want to modify my early Corvette valve covers either. I drilled and tapped an existing boss at the rear of the manifold (Edelbrock Performer) and used a mid-sixties Chevy pcv valve. I made a baffle for the underside and am using the front filler tube with a breather at the front. Works great.

 

I'll point out that where you live will be a factor. If you're in a dry, low-humidity climate a front-to-rear design will probably work fine. But if high humidity is common, you'll be more likely to have issues.

 

I've had a PCV valve in the valley pan where the road draft tube went on my 57 T-Bird for the last 26 years. I see no sludge build up when I do a valve adjustment. However, the car doesn't get a ton of miles and doesn't do a lot of idling.

On the 401, if you can find a pair of the Buick aluminum valve covers, you can have the modern PCV setup.

 

OEM 66-67

 

Where's the breather in that system?

 

The air filter is the breather, it connects to the tube under the distributor.

 

Since your 350 block doesn’t have the the rear vent you need to get a little creative and chop&drop has it. If you want to leave your filler cap without a hose to the underside of the air cleaner and hide the system I would personally do the fitting in the intake over the lifter/pushrod valley. With that said under that fitting you really should fab a shield/oil drain box so the PCV valve doesn’t **** oil. All this entails removing your intake to do this. This is the closest you will get to the 61-up system from Chevrolet. They found out later that rocker cover to rocker cover was far better.

My Y-Block Ford draws from the valley cover to the bottom of the carb where I have a fitting for a V100 PCV valve just like SBC’s did from 61-up. It happens to have a welded factory box under the valley cover.

For your Buick you can drill a hole in the valley cover and install a special grommet for a SBC rocker cover that doesn’t have a deflector and takes a standard PCV valve and hose it to the carb or under the carb.

It’s very easy to not screw up an old set of rocker covers if you think about it.
You will like having your garage not stinking after having your car out..

 

I too, have Corvette valve covers that I won't cut holes in. I posted my solution here before but never really had the car on the road to check it out. Running a SBC with an electric fuel pump so I figured that the old fuel pump location was open to the crankcase and a good spot to place the PCV. Welded my idea of a baffle to the back side of the doghouse plate, gutted out a rebuildable mechanical fuel pump with a clear path from the crankcase to the outlet port where I mounted the PCV valve. Now that I have the car on the road, there was oil all over the place. I reworked my baffle since I really can't see how the oil churns inside the engine. Hopefully I still have enough places for enough air flow. Went to put the dummy fuel pump back on and had oil all over my hands. There are two small holes on the sides of the pump I hadn't noticed before. In the pictures, I have them since plugged with Phillips head sheet metal screws. Now no leaks.

 

Old style block with a trash can separator

 

Only in the earlier models. The 8BA's had the vent on the fill tube (in the front), and the exit (road draft tube) right behind it. To get from the "in" to the "out", the air had to circulate through the entire engine.

The Ford engineers weren't sitting on their hands through WWII. The later engines are superior in many ways to the earlier ones, primarily in coolant distribution and crankcase ventilation.

 

I like the way Jim thinks!

Ben

 

So based on what I've gleaned/learned here's my plan:

• go with the front-to-back system (on both the SBC and nailhead)
• pull the valve covers occasionally to check for sludge build-up
• if sludge builds up uncontrollably I'll change back to valve cover-to-valve cover system; if doesn't just keep on keepin on

We plan to put LOTS of miles on Clarence (SBC) but not so much on the Model A (nailhead). Clarence miles will be mostly summer but some year-round. The nailhead will nearly always be summer driven.

Clarence will be for long range (comfortable) fun and the Model A will be for shorter "fun blasts" of probably less than 1K miles round trip each. We might or might not be able to rack up the miles that Bob K did or Denise(@hotrodladycrusr) and Roger(@40StudeDude)/Dan do but we're sure gonna try.

 

You got lots of input already and PCV systems are easy to explaore. However, 1 thing that has really been a blessing to engines and sludge formation is the oil quality we have today. Old waxy **** wadded up fast, but how sludged up is a newer engine after 150K miles? I'd bet a good cup of coffee it's not all due to case venting. I have a 300K mile O/T SUV that has very little sludge in the oil cap (the most likely place I'd see it). Granted I do always change the oil in that ol ***** evry 6K miles but still. Save your precious valve covers (not a snarky remark) and vent it through the valley as advised. Last time I looked there's holes leading up to the rocker arms for the push rods to get to em. You'll get plenty of evac.

 

@atch, I think you have a very practical approach to venting.
Happy rodding.
See you down the road.

 

Right or wrong, this is what I'm doing on my '32. It has a '68 block so no road-draft hole available in the back of the block for air in. I didn't want to drill a hole in the Offenhauser intake and actually like the old hot rod look of breathers in the Vette valve covers. I hooked up a PCV valve in line between the fill tube and the rear carb port (kinda hidden under the front carb linkage). I'm hoping it pulls a little air out of the crank area but am aware that most will probably come straight out of the valley.

 

It’s actually going to draw from the rocker covers vents thru the push rod holes. In the long run it’s from everywhere..

 

Plumbing mine into this I just found n the shop

 

Road draft tube I fabbed up to clear the fire wall. Keeping it traditional

 

When building your own system , remember to be sure the inlet air is filtered .
FWIW , most valve cover " breathers" do not filter air coming in , any packing in them is designed to keep oil in the engine ,not to keep dirt out .